In general, a clothes dryer includes two types: one is an exhaust type for drying clothes by introducing an ambient air, and the other is a dehumidifying type for removing humidity while circulating an inner air and condensing the removed humidity to a water drop state to discharge it.
FIG. 1 is a view showing an internal construction of an exhaust type clothes dryer in accordance with a conventional art.
As shown in FIG. 1, the conventional exhaust type clothes dryer includes: a drum 20 rotatably installed in a case 10 so that clothes can be dried therein; a driving motor (not shown) connected with the drum 20 by a belt 25 so as to rotate the drum 20; a heater 33 installed at an entrance of a suction duct 30 at the rear side of the drum 20 and heating a sucked air; and a blower 37 installed in an exhaust duct 35 at a front lower side of the drum 20 and forcibly discharging air used for drying clothes in the drum 20.
A door 15 is installed at a front side of the case 10 in order to put in or draw out the clothes.
A suction hole 21 is formed at a rear side of the drum 20, into which the ambient air heated while passing the heater 33 can be introduced through the suction duct 30, and an entrance 36 of an exhaust duct 35 is connected at the front side so as to discharge air used for drying the clothes in the drum 20.
Especially, the entrance 36 of the exhaust duct 35 is protruded to be slanted inwardly of the drum 20, and an electrode sensor 40 is installed on the protruded slanted face in order to sense dryness of the clothes.
The electrode sensor 40 is constructed such that two metal plates are positioned side by side and an electric wire is connected to each metal plate to thereby construct a circuit, so that by sensing a change in a voltage flowing through the both metal plates, a dryness degree can be determined.
When the electrode sensor 40 becomes short when clothes with much humidity are in contact with the metal plate, and when clothes with a little humidity after being dried are in contact with the metal plate, a voltage value increased, and thus, the dryness degree of clothes can be determined with the difference between voltage values,
The clothes dryness degree sensed by the electrode sensor 40 is inputted to a control computer (not shown) for controlling an operation of the dryer and used for various control operation for clothes drying.
In the conventional exhaust type clothes dryer as constructed above, as the driving motor is operated, the drum 20 connected by the belt 25 is rotated, and at the same time, the blower 37 is rotated.
As the blower 37 is rotated, the ambient air is introduced into the suction duct 30, and as the ambient air passes the heater 33, it is heated and introduced into the drum 20.
The heated air introduced into the drum 20, that is, the hot air, is heat-exchanged with the wet clothes to dry the clothes, and then, the hot air is discharged outwardly of the case 10 through the exhaust duct 35 after drying the clothes.
Especially, in the process of drying the clothes, when the drum 20 is rotated, the clothes being dried inside collide with the electrode sensor 40 protruded into the drum 20, and at this time, a voltage value of the circuit connected with the electrode sensor 40 is changed, so that the dryness degree of the clothes can be determined.
FIG. 2 is a graph showing a dryness degree sensing state using the electrode sensor in accordance with the conventional art.
With reference to FIG. 2, at the initial stage that the clothes contain much humidity, a voltage value sensed by the electrode sensor 40 is low, while as the clothes proceed with drying, the voltage value is gradually increased.
At this time, the dryness degree sensed by the electrode sensor 40, that is, the voltage value change, reaches a certain numeric value (5V in FIG. 2), the control computer determines it's a dryness completion time point and discontinues operation of the dryer.
However, the dryness degree sensing apparatus of an exhaust type dryer in accordance with the conventional art has the following problems.
That is, since the voltage change value according to the humidity of clothes is checked by the electrode sensor 40, the voltage change value is high at the initial stage and the middle stage, so that the clothes dryness can be accurately determined.
However, at the last stage of drying, since the voltage change value is low, so that it is difficult to accurately determine a time point of completion of the clothes dryness.